Habitat and Bird Community Change
At the Palomarin Field Station we have been monitoring birds and their environment since 1966. Since the beginning of our study, the area adjacent to the mist nets and banding station has undergone drastic habitat change, resulting in shifts in the local bird community. Tracking the changes in the habitat alongside the changes in bird populations at Palomarin can inform bird conservation as we learn more about what environmental factors are most important for certain species to thrive. Here, you can explore the habitat changes and bird community changes we have recorded through our long-term data collection.
Over 50 years of habitat transformation
During the 15 years before the field station was established, the land around Palomarin was partially cultivated for agricultural use and hosted many buildings. Since its inclusion in the nascent Point Reyes National Seashore in 1965, disturbance to the landscape has been minimal and the vegetation has gradually transformed.
In the earlier years of our study, the landscape at the field station was comprised of two distinct habitat types: the mist-netting and banding site was largely forested while the area adjacent, where much of our nest searching takes place, was dominated by short, open coastal scrub.
The vegetation across the study area has since grown in size and structure and has become a complex mix of mature scrub with tall coyote brush, poison oak, California blackberry, and a young, dense Douglas fir forest. We have documented the change in the average height of these firs over time, as well as an increase in the number of trees in the study area, and the height of shrub species like coyote brush.
Why is tracking habitat change important for bird conservation?
Bird species have individual habitat requirements and preferences, and can be affected by habitat change in a number of ways. They may find it easier or harder to find food, raise young, avoid predators, or survive extreme weather conditions. As the habitat at Palomarin has transformed, we have witnessed the open coastal scrub residents that once flourished here (such as White-crowned Sparrows) fade from the study area while more forest and mixed scrub species (such as Wilson’s Warblers and Swainson’s Thrushes) moved in. By studying how birds within a community respond differently to changes in their environment, we can learn what they need to thrive, to help inform and guide conservation efforts. Land management and restoration projects can benefit from this type of research by understanding how best to create an environment that supports a more resilient bird community.
Changes in the number of breeding territories
One way to measure the response of the breeding bird community to habitat change around Palomarin is the number of breeding bird territories. Since the early 1980s, nearly every day during the spring and summer, Point Blue staff and interns collect data on the movements and behaviors of breeding birds to create territory maps representing that season’s breeding bird activity. The number of territories provides us with a measure of how many breeding individuals of each species are present in the bird community.
Extra attention is paid to four primary focal species, which are also given unique combinations of colored leg bands so we can more easily identify individuals in the field: Song Sparrows, Nuttall’s White-crowned Sparrows, Wrentits, and Wilson’s Warblers. The number of Song Sparrow and Nuttall’s White-crowned Sparrow territories have declined, while Wilson’s Warblers and Wrentits have greatly increased.
We have found that Nuttall’s White-crowned Sparrows have stayed just as successful at raising young over this time period, despite the decline in their numbers. They strongly prefer to nest in patches of open coastal scrub that have become rare at Palomarin, and they may be seeking out their preferred habitat elsewhere.
New species join the breeding bird community
We have also seen changes in the rest of the breeding bird community, especially the addition of more species associated with mature forest and mixed scrub such as Wilson’s Warblers and Swainson’s Thrushes.
So far, our research has found that bird populations are more directly influenced by changes in habitat and weather or climate rather than interactions with other bird species. But we expect there to be an increasing number of new interactions between species as they move in response to habitat and climate change, and future research could continue to examine this question.
How did we collect these data?
During the breeding season (March-July), three interns spend their days stealthily tracking birds to map the boundaries of the territory each one calls home, as well as to find their nests and determine how successful each nest attempt is. The interns are trained in how to identify and follow birds by both sound and sight, as well as how to find and safely monitor their nests. A bird that sings in the same area day after day is considered a territorial individual. After months of recording the movements and territorial behavior of individual birds, we compile all of this data into territory maps for each species.
Each summer, we also collect vegetation data at 8 fixed points throughout the study area. The data helps describe the habitat succession as well as the proliferation and growth of the Douglas fir trees. At each of the 8 points, we record the size (height and width) and species of all woody plants along four 10-meter transects.
Plan your visit!
Although the Palomarin Field Station is currently closed to the public, we welcome you to plan your visit in the near future. Visitors can drop in and join our intern and staff biologists to learn how we collect this data — and hopefully see a bird in the hand! More information on visiting and scheduling groups.